This invention relates to a toggle press with two levers which are pivotably connected by means of a joint, the first of which is connected at its free end to a pressing tool, and the second of which is rotation-resistantly mounted at its free end on a shaft which can be rotated by a drive unit.
A toggle press comprises a toggle lever mechanism with two levers connected by means of a joint, whose free ends are connected with the associated machine frame on the one hand and with a tool or ram on the other. The ram can be moved in the direction of a workpiece by extending the toggle joint. The press can be driven by exerting pressure on the toggle joint, as well as by pivoting the lever mounted on the frame with the aid of a driven shaft. This invention is concerned with the latter type of construction.
Toggle presses can be built in a very stable fashion to permit the transmission of large forces. The design of a toggle press becomes complicated when workpieces of varying thicknesses require processing because the adjustment of the stroke and, in particular, the fine adjustment for adaptation to differing material thicknesses cannot be achieved without costly additional constructions. This is because, in the final phase of its movement through to complete extension of the two levers, a toggle press develops very high forces which can, in theory, be of an infinite order. A slightly wrong adjustment of a toggle press can therefore lead either to the destruction of the press, or to the application of insufficient machining force. Toggle presses are not, therefore, necessarily suitable for processes requiring only a relatively short working stroke applied with high force consecutive to a longish approach stroke.
There are prior art drive systems for presses whose stroke is composed of a larger approach stroke executed rapidly and with relatively low force followed by a short working stroke executed with high force. This is described with reference to a hydraulic-pneumatic press in the applicant's patent 100 51 042. The problem of adjusting the working stroke can be solved relatively easily in this case.
Hydraulic or pneumatic systems are not, however, available in every business, and in many cases, hydraulic drive systems cannot, or should not, be employed because of the constant risk of workplace contamination from leaking oil; in the food industry, for example, they are not generally permitted under existing legislation.